The invention relates generally to a method for forming a pattern of a semiconductor device that can control a fine critical dimension and improve an overlay characteristic of the device.
In the manufacturing of semiconductor devices, the resolution required in the semiconductor device has decreased beyond the minimum resolution that can be resolved using photolithography equipment.
For example, if the minimum resolution is 45 nm when an exposure process is performed using photolithography equipment, the semiconductor device may require a resolution smaller than 40 nm.
Due to the limit of the photolithography equipment, various patterning technologies have been proposed. Of these technologies, a patterning technique using a spacer has been widely used.
FIGS. 1a to 1g are cross-sectional diagrams illustrating a conventional method for forming a pattern of a semiconductor device using spacer patterning technology (SPT).
Referring to FIG. 1a, a nitride film 110, a first polysilicon layer 120, an anti-reflective film 130, and a first photoresist pattern 140 are formed over a semiconductor substrate 100.
The first photoresist pattern 140 is twice as wide as that of a final pattern.
Referring to FIG. 1b, the anti-reflective film 130 and the first polysilicon layer 120 are etched using the first photoresist pattern 140 as a mask to form an anti-reflective pattern (not shown) and a first polysilicon pattern 120a. 
The anti-reflective pattern (not shown) and the first photoresist pattern 140 are then removed.
Referring to FIG. 1c, an oxide film (not shown) is deposited over the resulting structure including the first polysilicon pattern 120a. A blanket-etching process is performed to form spacers 150 at sidewalls of the first polysilicon pattern 120a. 
The spacers 150 are formed to have a critical dimension (CD) that is the same as that of the first polysilicon pattern 120a. 
Referring to FIG. 1d, a second polysilicon layer 160 is formed over the resulting structure including the first polysilicon pattern 120a and the spacers 150.
The second polysilicon layer 160 reflects a step difference of the first polysilicon pattern 120a. 
Referring to FIG. 1e, an etch-back process is performed to expose the first polysilicon pattern 120a, so that the second polysilicon layer 160 remains between the spacers 150. The etch-back process is a dry etching process.
After the etch-back process is performed, the second polysilicon layer 160 remains on the sidewalls of the spacers 150. An additional etch process is required to remove the residual second polysilicon layer 160.
The entire second polysilicon layer 160 is etched in a large open area to expose the first polysilicon pattern 120a during the etch-back process. As a result, a pattern cannot be formed in a peripheral circuit region and an inter-connection region during a subsequent patterning process without forming a second photoresist pattern over the cell region.
Referring to FIG. 1f, a second photoresist pattern 170 is formed over the resulting structure, including the second polysilicon layer 160 and the first polysilicon pattern 120a. The second photoresist pattern 170 may be formed over a cell region of the semiconductor substrate to allow for patterning of the peripheral circuit region and the inter-connection region.
A process for forming a pattern is then performed on the peripheral circuit region and the inter-connection region (not shown).
Referring to FIG. 1g, the second photoresist pattern 170 is removed.
The spacers 150 are removed to form a fine pattern including the first polysilicon pattern 120a and the second polysilicon layer 160.
In the above-described conventional method for forming a pattern of a semiconductor device, residual polysilicon remains on sidewalls of the spacer during an etch-back process performed after forming the polysilicon layer, so that a subsequent process for removing the residual polysilicon is required. The entire polysilicon layer having a large open area is etched, so that a subsequent patterning process cannot be performed without forming a second photoresist pattern over the cell region.